A dual in-line memory module (DIMM) is a series of random access memory (RAM) integrated circuits mounted on a printed circuit board and designed for use in personal computer systems. A DIMM typically includes a number of independent sets (or ranks) of dynamic RAMs (DRAMs) that can be accessed simultaneously for a full data bit-width of the DIMM to be driven on an input/output (I/O) bus. However, each of the DRAMs within a DIMM is to have a unique ID.
The DRAM devices within a DIMM include a small number of configuration registers. These registers include key information, such as the desired operating speed of the DRAM. In a conventional memory system these registers are accessed simultaneously and are “write-only”. In more advanced memory systems, such as fully-buffered DIMM, there are several memory buffer devices, each with a larger number of registers and read/write access to those registers. Applications such as these require that each buffer chip or DRAM device, have a unique identifier, or address so the registers on that device can be read independently of other devices.